Electric pick-up



April 12; 193s.

A. F. SYKES ELECTRIC PICK-UP Filed Feb. 20, 1937 2 Sheets-Sheet l 'April 12, 193s. A. F SYKES 2,113,907'

ELECTRIC PICK-UP l Filed Feb. 20, 1937 2 Sheets-Sheet 2 Patented Apr. 12, 1938 UNITED STATES PATENT GFCE Application February 20511937, Serial No. 126,914

In Great Britain February 21, 1936 17 Claims' (Cl. 179-100.41)

This invention relates to electric pick-ups for playing so-called hill and dale sound records, that is to say to devices for translating into electrical variations sounds recorded in the form of variations in the depth of a sound record. In such dale pick-ups which shall not pick-ups a stylus or needle is arranged to run in the groove on the record and the movements thereof, induced by the variations in the depth of the groove, are translated into electrical Variations by microphonic, moving coil,l piezo-electric or other means known per se for translating movements into electrical variations.

As is obvious it is required, in an electric pickupg for hill and dale records, to arrange for the stylus to follow the contour of the bottom of the' groove in which it runs and, in known electrical pick-ups for hill and dale records it is usual to arrange the pick-up to oat on the record by the well known gravity action. Thus casual inequalities in the record are sought to be taken up by movements of the pick-up as a whole whereas, of course, recorded sound is required to induce movements of the stylus member of the pick-up relative to the main body structure thereof. Now a pick-up' is necessarily a relatively massive piece of apparatus and it will readily be appreciated therefore that this usual type of arrangement has serious defects, the most important being that the pick-up as a whole is free to bounce and its behaviour to the lowest acoustic frequencies and to casual deformities in the record is a matter of uncertainty; moreover the momentary elfect of transients may cause sudden displacements of the mean position which render it more difcult for the stylus to remain in proper contact with the sound wave constituting the bottom of the groove. It has been proposed to make use of a sliding shoe resting on the record and which supports the main body structure of the pick-up while allowing the armature to follow the recorded matter, but this proposal is obviously unsatisfactory, it being very diiiicult, if not in practice impossible to ensure that casual inequalities and deformities'in the record do not induce relative movement between stylus member and the main body structure of the pick-up while furthermore the use` of a shoe sliding over the surface of the record is obviously highly objectionable.

The present invention seeks to provide hill and present the defects of the known pick-ups already referred to and which shall be of high fidelity, robust and simple in construction and reliable in use.

The invention consists in a hill and dale pickup arrangement comprising in combination a stylus member which is free to move in the vertical direction and also has freedom in the horizontal direction, a main body structure from which said stylus member is carried, said stylus member being yfree to move in the vertical direction relative to said main body structure. Means for applying a substantially constant biasing force in the vertical direction between said stylus member and'said main body structure, translating means actuated -by movements of said stylus member in the vertical direction relative to said main body structure for translating said movements into electrical variations, and means IiXedly supporting said main body structure as respects movement in the vertical direction.

By the expression vertical direction as herein employed is meant the direction of the movements due to the hill and dale sound track at the bottom of a hill and dale record when the stylus is following such a track and by the expression "stylus member is meant the light member by which the stylus is carried and with and by which it is moved.

The translating means may be of any general nature well known per se, e. g. microphonic, electro-dynamic (moving coil) or piezo-electric.

The substantially constant biasing force is, in the simplest and preferred case, a spring of such length and construction that the spring force it applies is not appreciably varied by the small changes in length it undergoes as a resultof movements of the stylus member relative to the main body structure. Such a spring is herein termed a "constant force spring.

The freedom for the stylus member to move in the horizontal direction may be obtained by allowing such freedom between the stylus member and the main body structure (as by providing a suitable hinge arrangement with a vertical axis in the stylus member construction and fixing the main body member absolutely); or by incorporating a suitable hinge arrangement with a vertical axis in and between two parts of themain body structure; or by mounting the whole pick-up on a carrier member hinged about a suitable vertical axis so as to prevent vertical movement but allow horizontal movement.

It is important to note that in pick-ups in accordance with this invention the stylusmember is subjected only to forces from the record, the force oi' the spring or its equivalent and such reaction forces as are due to the translating means.y Since the stylus member is quite light and small and the force of the spring can be varied over a wide range this means'that the natural frequency of the stylus member regarded as an acoustically vibratory body, can be chosen at a suitably high value where a minimum of distortion is occasioned. This provides a great advantage as compared to the known pick-ups already referred to. I have myself previously proposed to construct a sound box (not a pick-up) for hill and dale records, the sound box having a diaphragm driven by cords from a stylus member pivoted on a horizontal axis and pressed way from the diaphragm by a rubber tension member.

Figures 2, 3, 4 and 7 represent another em-` bodiment in plan from above, plan from beneath, part sectional elevation and end view respectively; g Y Y Figure 5. illustrates Van alternative detail of construction for the stylus member and Figure 5a is a view taken at right anglesto Figure 5 and looking toward the plane of the sheet with respect to, Figure 5; Y v. Y Y

Figure 6 is a diagrammatic simplified view (notY Vto scale) provided to .assist in an under-V standing of the method of operation and Figure 6a is a detail sectional view of a pivot included in the embodiment shown in Figure 6;

Figures 8 and 9 illustrateva tion, Figure 9 showing to an enlarged scale the vertical pivot arrangement for the stylus member.

There are ,constructionalsimilarities,betweenY the pick-ups of the present invention and those of my previous Patent No. 2,038,687 and for this.

reason the reference numerals in the present drawings have been selected to correspondrwhere possible, with those adopted in the drawings of my said previous patent..

Referring to Figure 1, 34Y is a reproducer post of an Edison typecphonograph of the travelling,

mandrel type (see my previous Patent VNo. 2,038,687) equipped with a pick-up `in accordance with this invention. A projecting member arrangement 3|, 32 is held in the reproducer post 34 and Ya bracket A99rsupports .a vulcanized fibre block |00 which isY arranged as shown so that it can pivot about a vertical axis. 36. A cobalt Ysteel magnet 4 with polar extensions |9| and |02, a wound po-le a bobbin 9 and a Winding I0 constitute an electromagnetic translating system of well known type and with which co-` operates a stylus member l which carries, or part` of which acts Yas the movable magnetic armature of said system. The member Y'| is hinged freely about a horizontal axis at |03 and is composed of a rigid but light bar carrying a stylus aand a leaflikevextensionV to the rear (the extension is hidden in Figure 1) to which is attached` a spring |04 the tension of which may be varied by adjusting, in any convenient and obvious man'- ner, the degreegof protrusion of a plunger member |05 to which one end of the spring is attached. A thread |06 fixed to the member l Here,` however, the acoustic vibratory unit really ,in-v..

further Vmodifica-V passes up through a'hole in the member 3| and terminates in a ball or ring |01. The magnetic armature part of the member 1V or the magnetic armature member carried thereby (as the case may be) is or may be laterally enlarged neari. e. it may extend at right angles to the plane oi the paper in Figure l-the wound pole so that a desired large change of magnetic flux is obtained in the translating system'for a given vertical movement of the stylus despite the fact that the member l, regarded as a lever, has a mechanical disadvantage, i. e. the movement at the pole is less than'that Aat the record. After lifting the ball` |01 the record, which in this em- Y bodiment isa cylinder, is placed on the mandrel and set revolving. The ball is then released and on Vcontact of the stylus with the record 42 the thread becomes slack. Since the member 1 is Vpractically (neglecting the spring |04) the only vibratingf part and is very small in mass and as in addition the spring, |04 is asubstantially constant force .spring,thevstylus is able to follow in a vertical direction not only the acoustic vi brations, but also the casual deformities, the` main body structure of the pick-up being fixed as regards ,thev vertical direction. Further the stylus will be able tofollow the recorded Ysound atrlow Yacoustic frequencies and should not be disturbed by transients.V j

Thepick-up mayfeed into the usual amplier system (not shown) either directly, orV if desired, through a step up transformer (not shown). In Figure V1 the pick-up is shown as applied to a cylinder phonograph of the feed screw traversing motion type but obviously pick-upsin accordance with this invention may equally wellbe used for reproduction from hill and dale-discs or cylin ders and may be used on talking machines whether of the feed screw transverse type or not.

InV the construction of Figures 2, 3, 4 and 7 there is, employed a shellof moulded material, '|48, 'i9 and,8|` which accommodates an electromagnetic translating mechanimV compriislng magnet V.4, central =pole with chamfered tip Il, bobbin 9,7 winding I0, and composite polar extensionformedfromthe elements |08, |09 and H0, while the structure of the stylus member 1 includes a lever of channel type cut away at H2' and provided witha rearward extension H3 on ,which the spring |04 is hooked. A gunmetal nut |23 clamps the magnet 4 to the polar extension |08,V |09 `and V| |0,-the nut being formed atthetop as shown at ||6 to provide a top bear--Y ing for allowing pivoting action about the vertical axis39. A strut 23 is screwed to the element |09 and either yengages directly'with themagnet 4 or with interveningdamping material H4 such as boiled castor oil ofV a non-drying nature. This servesV to. consolidate the magnet structure. 82 isa sheet metal tab to which a wire from the bobbin 9 is soldered and which connects with a terminal I9, there being; of course, two tabs one for each terminal and for each end ofthe coil on the bobbin 9. copper bracket ||5 acts as a limiting ldevicein wellknown` fashion so that the stylus 8 is Vproperly centered for engagement with the record. The magnetic structure is supported in gate fashion to swing about theyertical axis 36by the bearing pin H6 and alower adjustable bearing Il. The construction. affords slight adjustments for height. H0 is avmember held by the screws` shown said screws passing through enlarged holes in said member so that by slackingv the screws,

A wire loop 43 soldered to a small adjustments in the position of member 1 may be made.

Figure 5 shows an alternative arrangement for the member 1. Here the arrangement comprises the member 1, partly milled out as at 8 for the sake of lightness, a strip I bent to V-form soldered to the said member, stylus the U-shaped wire 43 of Figure 4 and a leaf of sheet metal to correspond to the tail piece 3.

Figure 6 is not to scale, this ligure being provided to illustrate the operation of the mechanism and to show the nature of the hinging of the member 1 to the polar extension pieceV ||0. The rear of the member 1 is made with a radius concentric with the adjacent circular surface of the element l0 and is set closely thereto so that the gap between thesesurfaces does not change as the member 1 pivots. In Figure 6 only a single line is shown at the gap, though, strictly speaking, two circular lines should be shown one representing each side of the gap. The gap is so small, however, that it would only result in an unclear drawing were it sought to be shown. The form of pivot is shown in the small detail view forming part of Figure 6. Here a bush |20 has a gunmetal insert |2| to form a shouldered bearing pin which, by preventing direct contact between the magnetized surfaces, avoids concentrated magnetic forces likely to introduce objectionable friction effects (sticking). The region |22 and the spring |04 may be covered with petroleum jelly to damp out oscillations in the coils of spring and if desired the whole region may be provided with a light cover. Similarly to protect the pick-up mechanism from mechanical damage a spider, cover, or grating, may be added so that practically nothing more than the stylus protrudes. Adjustment of the spring tension can be elfected by slacking the set screw shown in Figure 6 and moving the bent arm |05, to which the spring is attached, either in or out. The stylus 8 is represented as in contact with' a cylinder record 42 shown dotted. In the absence of the record the stylus lever rests on the bottom of the U-shaped Wire 43 and the range of action takes into account any variation of diameter of record likely to occur in practice together with any reasonable amount of wobble or eiect due to warping. For this state of aiairs to be realized the setting of the armature in relation` to the central pole must not be too close and the spring must have a considerable degree of compliance, that is to say within the amplitude of motion desired the control force on the armature should not change very greatly otherwise the governing of the reproducing machine may not be good enough. For celluloid cylinders with 200 threads per inch a force of about two ounces on the stylus is provided which implies the use of a spring capable of being stretched to produce from eight to ten ounces. I nd that a spiral spring made from piano wire is` quite suitable. With this type of mechanism it is the acceleration at every point on the sound line of the record that has to be provided for. Hence it is very desirable to make the extremity of the stylus lever and the diamond point or other stylus itself together with its mounting very light and rigid.

In Figures 8 and 9 the vertical axis for allowing horizontal freedom for the stylus member is actually in that member instead of being provided by a hinge in the main body structure. Here the stylus member structure 1 consists of two parts I I la, I Hb hinged to one another about a vertical axis |24 which replaces the vertical axis 36 of the previous gures. |25 is an embracing strap with a tag |28 for receiving the spring |04, the strap being xed at its ends to the member |||b as by soldering. The hinge comprises a top bearing pin |26 integral with the part |||bl and a bottom bearing pin |21 integral with the squared trunnion member |29, the member la, which is V-shaped in plan, having its open ends of the V xed to the squared sides of member |29.

What I claim isz- 1. An electric pick-up arrangement for hill and dale sound records, comprising in combination a main body structure, a stylus member carried from said main body structure and which is free to move in a vertical direction relative to said structure, Said stylus member being Y also free to move in a horizontal direction, means applying a substantially constant bias force between said main body structure and said stylus member to bias said member away from said structure, translating means actuated by vertical movements of said member relative to said structure for translating said movements into electrical variations, and means xedly supporting said structure against movement in a vertical direction.

2. The invention as claimed in claim 1, characterized in that the support means for the main body structure provide freedom of movement in a horizontal direction for said structure, whereby said structure can move horizontally to allow the :freedom of movement of the stylus member in a horizontal direction.

3. The invention as claimed in claim 1, characterized in that the main body structure includes two portions hinged to one another on a vertical axis, whereby one of said portions can move horizontally to allow the freedom of movement of the stylus member in a horizontal direction.

4. The invention as claimed in claim 1, characterized in that the stylus member comprises two portions hinged to one another on a vertical axis.

5. The invention as claimed in claim 1, characterized in that the means applying the substantially constant bias force is a substantially constant force spring.

6. The invention as claimed in claim 1, characterized in that the stylus member provides a mechanical disadvantage as between movement, in avertical direction, of the stylus and corresponding movement of the `moving member of the translating means.

7. An electric pick-up arrangement for hill and dale sound records comprising in combination a main body structure, means for fixedly supporting said structure against both vertical and horizontal movement, said structure including two portions one of which is fixed to said supporting means and the other of which is hinged to said one portion on a vertical axis, translating means incorporated in said other portion said means having a movable armature and being adapted to translate movements thereof into electrical variations, means including a stylus member for producing movements of said armature in response to sound waves on a hill and dale record, said stylus member being pivoted on a horizontal axis and carrying a stylus, and a substantially constant force spring biasing said stylus member about its pivot and away from the main body structure.

B. 'Ihe invention as claimed in claim '1, characterized in that the armature is between the stylus and the pivotal axis of the stylus member.

9. The invention as claimed in claim '7, characterized by the provision of manually operable means for moving the stylus member in a vertical direction against the bias of the spring.

10. The invention as claimed in claim '7, char-V acterized in that the pivotal axis of the stylus member is between a point Where the spring is attached thereto and the stylus.

11. The invention as claimed in claim 7, characterized in that said other portion of the main body structure isA housed within a cover member forming part of said one portion of said structure, said other portion being pivoted on a vertical axis provided by bearings in said one portion and corresponding bearing members in said other portion.

12. The invention as claimed in claim l, characterized in that limit means are provided for limiting c the movement of the stylus member away from the main body structure.

13. The invention as claimed in claim 7, characterized in that limit means are'provided for limiting the movement of the stylus member away from the main body structure.

14. The invention as claimed in claim 1, charaoterized in that said means for applying the substantially constant bias force are adjustable.

15. The invention as claimed in claim 7, char- Vavcterized in that means are provided for adjustingthe spring force.

16.r The invention as claimed in'claim 1, characterized in that the translating means are electromagnetic. Y

17. The invention as claimed in claim 7, characterized in that the translating means are electromagnetic. Y

ADRIAN FRANCIS SYKES. 

